1. Field of the Invention
The present invention is directed to a meter prover or calibrator to detect passage of a traveling liquid displacer in a pipe-type meter prover. In particular, the present invention is directed to a meter prover or calibrator that will operate in dirty service or non-lubricating service conditions.
2. Prior Art
Liquid passing through a pipeline conduit is often measured by a meter or meters that are installed in the pipeline. The accuracy of the meter or meters on the pipeline is an extremely important consideration. In the petrochemical industry, for instance, title to the oil or petrochemical products may pass from one party to another with the passage through a pipeline. Likewise, the price is often determined by the amount of oil or petrochemical products delivered as determined by the meter. Accordingly, it is extremely important for the meter or meters to be accurate.
Additionally, it is common practice for a contract for the sale of the oil or petrochemical products to call for periodic proving, or calibration, of the meter. Prover devices have been devised over the years in order to calibrate the meters.
There are various types of provers such as a volumetric tank prover having a calibrated tank or vessel with a sight gauge and scale to read a metered volume. Additionally, there are unidirectional provers, which are positive displacement type provers, where flow of fluid is in a single direction moving a displacement sphere. The flow of fluid and the displacement sphere travel in a single direction by means of a transfer chamber or interchange. Additionally, bidirectional provers utilize a positive displacement type prover where the flow and the liquid displacement sphere travel in alternate directions by means of a four-way diverter valve.
In one type of a bidirectional prover, liquid flow goes into a four-way diverter valve and forces a sphere displacer into a pipe section which seals against the pipe walls. In one arrangement, an inflatable sphere of urethane, neoprene or nitrile is utilized. The sphere is inflated from 2% to 4% larger than the pipe inside diameter. The sphere displacer passes between two detectors. The volume of liquid between the detectors is known as the calibrated volume. This calibrated volume is then compared to the volume indicated by the meter in order to determine a meter factor as follows.       Meter    ⁢          xe2x80x83        ⁢    Factor    =            Acutal      ⁢              xe2x80x83            ⁢      Calibrated      ⁢              xe2x80x83            ⁢      Volume              Metered      ⁢              xe2x80x83            ⁢      Volume      
There are various types of detectors. One type of detector device is disclosed in Assignee""s U.S. Pat. No. 4,481,806. A spring loaded piston extends from a barrel bore into the prover pipeline. As the displacer sphere passes the detector, it causes the piston to move axially toward a proximity switch which makes contact or makes a switch.
The prover, once liquid is inserted therein, is under pressure. Accordingly, the bore of the detector in which the piston operates will likewise be pressurized to the same degree. Accordingly, the detector must provide for pressure balancing and pressure relief of the bore.
In some cases, the piston will be lubricated or will utilize the oil in the system for lubrication. Other applications include non-lubricating services, such as LPG service where the fluid does not provide lubrication of the detector. In other situations, known as xe2x80x9cdirty servicexe2x80x9d, solids, such as metal particles, sand and other solid materials, will be transported in the fluid. One example would be a crude oil containing a certain amount of solid particles. Solids may also be present from construction debris, deterioration or abrasion in the pipeline. This may cause the piston or the switch internal bore to be marred. Over time, if the piston or bore is marred, it will interfere with its operation. Accordingly, it would be advisable to seal the interface between the piston and the bore from solids or other debris.
Likewise, it would be desirable to periodically flush the bore of any fluids to provide pressure relief and to also clean the barrel.
The present invention is directed to a detector for a meter prover having a pipe segment and a displacement sphere. The detector includes a barrel formed from a number of components, including a base affixed by welds or otherwise to the external surface of a pipeline of a prover. The barrel includes a removable adapter having a seal, such as an O-ring, between the adapter and the base to form a fluid tight seal. The barrel also includes a hub and a face plate. The base, the adapter, the hub and the face plate combine to form a cylindrical bore. A cylindrical piston is mounted in the bore. In the rest position, one end of the piston extends into a pipe of the meter prover.
The hub includes external threads to mate with and engage a housing having internal threads. The hub also includes an internal threaded opening to receive a magnetic proximity switch.
Juxtaposed between the proximity switch and the piston is a spring, such as a coil spring, to urge the piston away from the magnetic proximity switch.
A pair of seals or wipers, such as O-rings, surround the piston to form a fluid tight seal between the bore and the external surface of the piston. The seals or wipers reside in recesses formed into the adapter so that the wipers prevent accumulation of solids, and provide smooth operation.
The piston also includes a fluid passageway through the center axis of the piston. As the sphere moves, it displaces the piston axially towards the proximity switch. At the same time, fluid in the bore will be moved or flushed from the bore, through the passageway, and back into the prover.
As the sphere passes the piston, it may have a tendency to seal the end of the piston. A plurality of pressure equalization ports are provided to provide pressure relief and allow fluid to escape therethrough.